The electromagnetic spectrum
ELECTROMAGNETIC SIGNALS AND SPECTRUM All signals used for communication are part of the electromagnetic spectrum and those that are not are based on kinetic energy (such as sound). All energy in the universe travels in waves and those waves radiate outwards from a source, just as waves ripple outwards from a stone tossed in a pond. ''' '''All radiation is said to have wavelength, amplitude, frequency, phase, and power. Everything from gamma rays all the way down through the visible light spectrum to radio waves are all electromagnetic energy and differ primarily in frequency. Electromagnetic waves are frequently represented mathematically using a sine wave on a cartesian graph (graph with the red wavy line below). A sine wave begins with a high value at the origin (where the X and sin X cross in the graph below), rises, falls and then returns the “X” axis. This single sine cycle is said to pass through 360 degrees of phase. When represented on a polar-rectal graph, you get a circle (360 degrees). In polar rectal coordinates, the values are a distance from the origin plus an angle from 0 degrees. POLAR CARTESIAN Below is a graph that illustrates a specific frequency at 1 hertz. It shows it's amplitude, its frequency (1 hertz per second) and its phase value at several points in time between zero seconds and 1 second. HISTORY OF ELECTROMAGNETIC SPECTRUM The history of the electromagnetic spectrum is the history of the discovery of the electricity and magnetism, and as such, the history of the human technology advances. During a long period of time, light was the only part of the electromagnetic spectrum that was known. The ancient Greeks recognized that light travelled in straight lines and studied some of its properties, including reflection and refraction. The study of light continued and in the 16th and 17th centuries there were conflicting theories which regarded light as either a wave or a particle. The first discovery of electromagnetic waves came in 1800, when William Herschel discovered infrared light. He was studying the temperature of different colours by moving a thermometer through light split by a prism. He noticed that the highest temperature is beyond red. He theorized the temperature change due to ``calorific rays´´, a type of light ray that could not be seen. In 1801, Johann Ritter worked at the other end of spectrum and he called ``chemical rays´´, light rays that introduced certain chemical reactions, behaved similar to visible violet light rays, but were beyond them in the spectrum. Later it was called ultraviolet radiation. Electromagnetic radiation was first linked to electromagnetism in 1845, when Michael Faraday discovers that light propagation in a material can be influenced by external magnetic fields. During the 1860s, James Maxwell developed four particular different equations for the electromagnetic field. These equations demonstrated a connection between the two electricity and magnetism, involving the velocity of light. Maxwell's Equations are used today as the basis of electromagnetic theory. Maxwell makes a prediction about the connections of magnetism and electricity leading directly to the prediction of electromagnetic waves. In 1886 the physicist Heinrich Hertz demonstrates the existence of electromagnetic waves and built an object to generate and detect radio waves. He also found that radio waves could be transmitted through different types of materials and were reflected by others (the key of the radar) In 1895, Wilhelm Röntgen noticed a new type of radiation, called x-rays. This type of radiation is able to travel through any part of the human body until the bones. This x-rays are used mostly in the field of medicine. The last portion of the electromagnetic spectrum was filled in with the discovery of gamma rays, rays emitted by radiactive particles. This discovery occurred in 1900 by Paul Villard, identiying them as a new type of radiation consisted of particles. In 1910 a British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914, Ernest Rutherford and Edward Andrade measured their wavelengths and high frequencies. ''' '''Thanks to the scientific advances, nowadays we know many applications of the electromagnetic spectrum, covering a wavelength range from 10,000 km to 10-14 m., and a frequency range from 1 Hz to 1026 Hz. Applications are very numerous. For example, we have the X-rays for medicine purposes, the night vision cameras, microwave ovens and radio communications (AM and FM radio) and mobile communications. ' ' James Clerk Maxwell Wilhelm Röntgen Heinrich Hertz Ernest Rutherford Spectrum characteristics The electromagnetic spectrum is formed by all the different types of electromagnetic radiation. We can distinguish inside the electromagnetic spectrum 8 main groups which are: 1-Gamma radiation 2- X-Ray radiation 3-Ultraviolet radiation 4-Visible radiation 5-Infrared radiation 6-Terahertz radiation 7-Micro wave radiation 8-Radio waves. In this part of the wiki, we are going to learn the main characteristics of the electromagnetic waves and which ones are used for classifying the waves into one group or other. Electromagnetic waves have 6 main characteristics: 1-Crest: The higher point of the wave ' '''2-Trough: Is the lowest point ' '''3-Amplitude: This is defined as the height of the wave measured from the crest to the trough. It is measured in power(Electron volts) 4-WaveLenght: This is the distance between to equal points in the wave. It determines the position of the wave in the electromagnetic spectrum. It also determines the shape of the wave, if it is more sharped or more plain.it is measured in distance (meters).It is represented by a Greek letter. 5-Period: The time it takes for a wavelength to pass a stationary point. 6-Frequency: This is the number of waves that pass a certain point in period of time. It is measured in time (Cycles per second) Here you can see some of the elements of the electromagnetic wave. Electromagnetic spectrum bands The electromagnetic spectrum is divided in different ‘bands’, this is, sections with a similar frequency, wavelength and energy. Note that the higher the frequency the higher the higher the energy and the smaller the wavelength. All of them are electromagnetic waves, waves that need no media for their transmission. These bands are, from lower to higher frequencies: '-Radio waves: radio signals are simply the signals you receive with your radio. We have sub-bands inside radio waves, which include medium and long radio frequencies. They vary from 30 kHz to 1 GHz.' '-Microwave: this is the type of wave that cook heat your food inside a microwave oven, by making molecules rotate, generating heat. This are found in frequencies between 1 and 300 GHz' '-Infrared: these is the frequency just below what our eye can see, this is the frequency which is used in the night vision glasses, because all objects emit it. It ranges between 300 GHz and 384 THz' '-Visible light: this is simply the light you can see. All visible colours (red, blue, green…) are inside this band, although each has its specific frequency. It ranges from red (smaller frequency) to violet (bigger frequency). Below red we have infrared and above violet we have ultraviolet, none of them is visible to our eyes. This band ranges between 384 and 789 THz.' '-Ultraviolet: this is the type of frequency that the sun emits, goes through the atmosphere and burns your skin. It ranges between 789 THz and 1.5 PHz.' '-X-rays: this is the frequency that is used in the hospitals to make radiographies, because X-rays go through many materials. It goes from 1.5 to 30 PHz.' '-Gamma rays: this is the most energetic and highest frequencies of all. It is emitted in nuclear reactions and in some astrological events, like the explosion of a supernova. It has a bigger frequency than 30 EHz.'